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    #page-container .header{
        height: 46px; line-height: 46px; text-align: center; font-size: 16px; font-weight: bold;
        color: rgba(0, 0, 0, .86); position: relative; border-bottom: 1px solid #f1f1f1;
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    #page-container .header .back{
        position: absolute; left: 20px; top: 0; height: 100%; font-size: 12px;
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    #page-container .header .user-btn{
        position: absolute; right: 20px; top: 0; height: 100%; padding: 0; font-size: 12px;
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    #page-container .context .cover-view{
        height: 150px; position: relative; background-size: cover; background-position: center center;
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    .cover-img{
        height: 100px; width: auto; position: absolute; left: 20px; bottom: 0;
        border: 1px solid #fff; 
        border-bottom: 0;
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    .unread-message{
        height: 20px; line-height: 20px; font-size: 12px; background-color: #f7c81b; color: #fff;
        text-align: center; width: 100%; position: absolute; left: 0; top: 0;
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    .infos{
        padding: 0 20px; font-size: 14px; line-height: 36px;
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    <div id="page-container">
        <div class="header">
            <span class="back">返回首页</span>
            <span class="user-btn">消息中心</span>
            《真·WebWorker》
        </div>
        <div class="context">
            <div class="cover-view J_CoverView">
                <span class="unread-message J_MessageTopic"></span>
                <img class="cover-img J_CoverImg" src="./cover.jpeg" />
            </div>
            <div class="infos">
                <p>本课程用来学习webworker在实际工作中的用途</p>
                <p>webworker不可以操作DOM, 但是可以发请求</p>
                <p>webworker内不要频繁进行打印，会卡UI进程</p>
            </div>
        </div>
    </div>
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<script src="./demo.js"></script>